A position sensitive detector (PSD: Position Sensitive Detector) is a PIN-type photodiode sensitive to the position of a light spot from the light incident to a photosensitive surface, which photo sensitive detector is consisted of a P layer, an I layer and a N layer by a planar diffusion manufacturing process and is sensitive to an incident light in the two directions perpendicular to the plane of the detector. It is widely used in a non-contact laser displacement detecting system owing to its advantages of a high resolution, good applicability, quick response speed and simple circuit structure in the subsequent processes.
The PSD and CCD are widely used in motion control systems with preciseness of micrometers, and by each of the PSD and CCD, a six-degree-of-freedom displacement of the moving platform is calculated with multiple measurements. They both have advantages and disadvantages. In contrast, the PSD has the advantages of a high resolution, simple circuit structure in the subsequent process, quick response speed and no dead zone, and the disadvantages of poor linearity and limited measurement range. Regarding accuracy and real-time performance, the PSD is more promising.
The range of a moving platform is limited due to the limited measurement range of PSD. Therefore, in a large-range moving system, other displacement sensors (electric eddy current sensors and grating ruler, etc.) are cooperatively used for measurement to improve the measurement range of the PSD measuring system and increase the moving range of the moving platform. However, different types of measuring elements may increase the difficulties of signal communicating and processing.